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User talk:Nicholas Watts
Welcome! Nice to see you here! I added your "Washer locking strategies" page to two categories, "Torsion" and "Washer", so that it shows up correctly on the category hierarchy page . Feel free to copy and paste stuff from your blog to the Wiki - it will be much easier to find from here than the depths of the blog :). Also feel free to add your pages to applicable categories (see above link); you can do it directly from the edit page. If you need any help with editing the Wiki just let me know and I'll try to assist. Anyways, a month or so ago I finally finished my new workshop, which in turn allowed me to resume my historical shooting weapon projects in full - the cheiroballistra included. This week I've ironed out most of the minor kinks in the ballista that prevented me from attempting pullback that would produce over 70 joules of energy (see this blog post). A few small fixes still need to be made, but no blockers remain. I'll write a blog post about this in the coming days, hopefully with improved results. The goal is to get 150 joules out of the weapon, but I will probably be content with less. After all, the cheiroballistra weighs only about 8 kilos. (Posted by Samuli) ---- Thanks Samuli. I must get stuck into Wiki so I can add those diagrams to make the vernier plate argument easier to understand. I wonder if there is a way to copy my blog entry outright rather than having to reassemble it for Wiki. That being said, I'd be interested to hear what you think about the placement of those four holes on the Elenovo end cap. Surely they are too close to the spring hole to make any sense as locking holes for the washer pins? Glad to hear you are back in business making ballistas. Best regards, Nick I just noticed that we need to add four tildes at the end to add a signature to our postings. Without a signature it's a bit difficult to distinguish between who is saying what :). Anyways, do you have a link or a reference to the Elenovo end caps? I can't recall reading about them. I remember you talking about the vernier plates, and I have no opposition against them, if they make sense in some particular machine. Mine doesn't have them and doesn't seem to need them. As for the cheiroballistra, I'm now restringing the torsion springs to get higher pretension (250hz -> 350hz). I'm doing this because I hit a performance wall yesterday at 75 m/s, 30 gram bolt and 85 joules. Some people might be happy with power level, but I'm not, even though a 10-gram bolt would fly pretty far at its ~95 m/s velocity. Anyways, the wall seems to have been caused by excessive cord/arm angle. In other words, rotating the arm starts stretching the cords too much too early, because it has less mechanical advantage than it would with less washer rotation. In other words, with zero washer rotation the arm can bend the cords trivially, as they're vertical and look like an "I" if you will. These cords can be moved easily sideways, because on unit of arm movement stretches the cords very little. As washers are rotated, form of cords approach a ">", and the arm has to stretch them a lot more to move them one unit sideways. So this is in my opinion what is causing the stacking of the torsion springs (as opposed to stacking of the "bowstring", which is another topic. I hope this explanation made some sense :). Anyways, the wedge/shim/pin system for attaching the field-frames is working perfectly, so I'm pretty sure that's probably the "right" way to do it. Simple, cheap and functional. If you have any comments about it I'm all ears. I'm soon running out of parts that break and things that don't work right... Samuli.seppanen (talk) 17:30, September 13, 2015 (UTC) The paper that covers the Elenovo horde is by Kayumov and Minchev. It is called, "The kambestrion and other militarty equipment from Thracia." Google will pop it right up. I found two types of "stacking" in my testing with Firefly. The first is the usual type found in archery where the limb of the machine is put into an increasingly unfavorable angle of leverage relative to the bowstring as it nears full draw. This is another reason why I have eschewed long draw lengths in inswingers. This kind of stacking was very obvious when I had Firefly up to 110 degrees limb rotation. ' I wonder if this phenomenom is a counter to the theoretically greater energy storage of big limb rotations. '(I have put this last sentence in bold because I'm hoping you can provide some clarity. I'm no math wiz.) In the artwork and math papers I see online many people seem to rave about big rotations as storing more energy. Maybe with longer springs? I don't know.... The other type of stacking I've encountered is exactly as you so aptly described with the "I" vs. the ">". The latter essentially being "Philon's horrible huddle". (A blog post from ages ago.) The only cure I know is to add much more linear tension before attempting your rotations. Are you applying a winch or something to stretch the spring out straight? Even with your small machine it probably needs about a ton of linear stretch locked in with..... locked in with what? Do you have a wedge system for the cross bars, or what? Anyway a lot more linear tension is the only fix I know of if your machine has got a case of the ">'s". Other than reconfiguring everything for much longer springs. But, I'm guessing that is beyond the scope of what you want to do right now. I just remembered, your machine does not have winch to cock it right? Perhaps those numbers I gave above are too stout for a belly cocker. It's a puzzlement that's for sure. I don't know what you can do right now other than up the linear. Good luck, Nick. 04:11, September 14, 2015 (UTC) I just remembered this part of a posting from Aug 12 2015, called "Hence the following". Maybe it will help. Incidentally, my dreaded swamp of a blog is easier to navigate now it has an archive function. (3) This next one is a bit tricky. I say that because Firefly has only ever tested one particular length of spring. With longer springs perhaps she would do a better job of using the 120 degrees (or whatever it is) of extra limb rotation depicted in the artwork. The longest limb rotation I ever tried with Firefly was 110 degrees and the performance was fairly abysmal. The formula that I hit upon for getting power out of Firefly was pretty simple and it favored much less limb rotation. The formula goes like this: if the tension on the bowstring is really taut in the at rest position, power is excellent. To have this extra tautness in the at rest position it is necessary to have the bundles cranked up very high with rotational pre-tension. With Firefly’s length of spring, this tautness can only be achieved with limb rotations of about 45 degrees. That is because when the rotaional pre-tension is up this high, the draw weight starts to stack heavily at around 45 degrees. To put it plainly, she ain’t a going no further. Big limb rotations and long draw lengths are kind of a non-starter for Firefly, fortunately however, that does not necessarily matter when it comes to generating velocity with inswingers. Our experiments have shown that it is that final snap of the bowstring as it closes the power stroke that is responsible for a lot of the projectile’s final velocity. To put it another way: loose, at-rest string with Firefly using 110 degrees of limb rotation and her shots were only puddling along at a meager 225 fps. Very taut, at-rest bowstring, with a short 45 degrees of limb rotation, and she was hammering the clouds at 360 fps and more. ………So anyway, our current prejudice on this matter suggests that really fast inswingers do better with much less limb rotation than is shown in the paper’s artwork. Deep down though, I intend to remain agnostic on the matter because the case for greater limb rotation needs more exploration than I’ve given it so far. Go figure…. Nick 04:45, September 14, 2015 (UTC) ---- Thanks for the reference to "The kambestrion and other militarty equipment from Thracia" - I'll have a look later today (need to do paid work first). And thanks for the other tips also! I pretension each cord the "classical" way using a stretcher which I designed: * Making the stretcher * Making the clip (work in progress, but the main idea should be apparent) * Stretcher usage (lacks descriptions, but I'll add those during the upcoming restringing) And for some additional technical details: * Tapering end of the spring cord * Three-ply eye splice (I recall you suggested this technique, and it works perfectly, thanks!) Pretensioning the cords to whatever tightness I want is no issue. I just started with a fairly small amount of pretensioning (250hz) to see how the nylon cord holds together. Given that your experience reinforces my "I" vs. ">" theory, I will give 350hz a go, and go beyond that as necessary. I'm sure that the higher the frame is, more rotation one can get without the ">"-stack, simply because it takes longer for the ">" to form. There's a summary of height/washer inner diameter rations here: * Calibration formulae and archaeological finds Cheiroballistra has the relatively highest frame there is, which in my opinion points to the fact that it used more rotation than the other (larger) machines. This makes perfect sense in a stomach-cocked weapon like mine, where you need to limit the maximum draw weight, yet feed in as much energy as possible. So, one basically needs as long draw as possible. With my current setup where the arms point slightly (10 degrees?) outwards at rest, at "full minus 14cm" (59cm) draw the string angle is about 90 degrees. Getting 7cm more draw without string angle stack is definitely doable. Beyond that the bowstring starts to pull the arms out of the bundles, which has historically been somewhat of a problem. That said, in those cases the pretensioning levels have been lower than the current ones. Samuli.seppanen (talk) 06:00, September 14, 2015 (UTC) ---- Hi Nick, Just in case you didn't notice, I cleaned up formatting on the Washer locking strategies page. Now it looks pretty professional. I also took a look at the "Kayumov & Minchev" article and the Elenovo hole carriers. The placement of the four holes does look odd, in particular the distance from the hole in the hole carrier. That said, there is quite a lot of area where the holes overlap, that is 10-14mm from the hole carrier's inner rim. That would have been sufficient to lock the washers in place. This is the same kind of impreciseness I've noted in my own forged washers and hole carriers: nothing really fits exactly, just "about so", so you need to adapt by making holes bigger and by using only one retaining pin instead of two. If one pin is used, then we also don't need "pairs" of holes, and can align the holes in the hole carrier slightly offset. This way the four holes in the Elenovo hole carriers would give more granularity than is immediately apparent. If I were you, I'd measure the angle of the holes and see if the are aligned in pairs or not. That might give a clue whether vernier plates are required for rotational granularity or not. That said, the pin holes are pretty close to the hole carrier's inner edge. I'm not sure if that's really an issue, except that the pin holes would have to be fairly close to each other in the washer. In my opinion, the primary advantage of the vernier plates is that they allow increasing the spring diameter for a given field-frame. However, there had to be some other advantage, too, because instead of making more parts, the artificer could have just made the hole carrier (and thus the frame) slightly larger and end up with the same bundle size with less work. The fact that washers then looks "tiny" is just aesthetics. In the case of cheiroballistra, the measurements indicate that the washer was placed directly inside the hole carrier, not on top of a vernier plate, which would be a "Missing part" anyways. We need to keep in mind that the Romans were not given a field-frame and told "make this field-frame as powerful as possible", which is what we're doing :). The vernier plates may also have been useful if made from thin steel. This would have made exact fit with the washer core easier, because the hole in the plate could be more easily filed to correct form. However, this theory goes out of the door because you'd still need to drill the holes for the retaining pins through it and the hole carrier, so not much is gained. I'm not sure if the vernier plates would have been that useful in adapting the washers to different field-frames. The problem is that you'd still need to have the holes in the hole carriers at exactly the same places for that to work, or you'd need to poke new holes to the hole carrier every time you switch field-frames and soon the plates would be swiss cheese unless the placement of the holes in the hole carrier was exactly the same in all field-frames. And if such preciseness was available to the Romans, why didn't they just make washers and hole carrier fit exactly? Anyways, that's some food for thought for the both of us :). I may have forgotten some of your vernier plate arguments, so feel free to correct me. Samuli.seppanen (talk) 07:39, September 15, 2015 (UTC) I just got through welding up the first Elenovo field frame. Looking at those 4 holes in the end cap in person, I feel even more bound to idea that they were not used for the washer pins. They are just too close to the spring hole to make any sense for this old tool and die maker. The logic of the layout I'm suggesting should be apparent if you bear down on that black diagram I sent you. Also, the obvious beefiness of the Elenovo field frame does not argue for smaller washers and smaller springs. I guess, for me, it really is a matter of elegance. Mature technologies pride themselves on maximizing all aspects of their design. Look at how little space is wasted under the hood in modern cars compared with a model T or something. By definition, the Orsova and Elenovo machines are mature technologies. I see this whole enterprise as an exercise in following certain thematic elements that are apparent in the artifacts themseles. Power, elegance, no wasted space, it's all of a piece don't you see? Here is a little blurb I was working on for the blog. I was trying to set some guidelines for historical ballista making that would keep things in bounds as experimental archaeolgy. Honoring the artifacts by deducing the themes apparent in their design is where it is at for me. Of course, that doesn't mean we all have to reach the same conclusion. But a tally of how certain designs might make the machine perform better (and be more elegant) seems a better way of triaging the evidence than leaning towards interpretations that yield less performance and wasted potential. The blurb..... It seems to me that there is only one unassailable starting place if you wish to build a historically accurate iron frame ballista. That is to simply duplicate, both dimensionally and materially, a particular set of artifacts that strike your fancy. After that it is largely a matter of trying to deduce what themes of design are implied by the artifacts themselves. (Loops and tangs, implies wedges, implies take-apart. Extra beefy stanchion, implies extra beefy Kamerion.) These "reconstructed" ancient machines that people are building these days, might be more correctly called "reimagined" machines. And there is nothing wrong with that from a scholarly perspective, just so long as the claims about what the machine represents are closely qualified. Given that there are no completely intact, ancient ballistas for us to study, it follows that any modern analog will be deficient in direct proportion to what is missing. Because I personally have no way of verifying if a particular ancient text matches up with a particular random artifact, it has always seem prudent to me to focus my attempts at "reimagining" on whatever could be deduced from the artifacts themselves. And with that in mind there is no better starting place than an exact-as-possible duplication of the artifacts. Any attempt to change, or alter without qualification, the starting place given by the artifacts should be grounds for instant dismissal. There is inevitably a lot of development needed to complete a modern historical ballista. This development work must be given more leeway than the duplication phase or no new machines would ever get built. For example, I am going to use a TIG welder to connect the joints in the Elenovo field frames. How much better would it be if all the joints were forge-welded like the original. Much better I should think. Or iron ore taken from the same quarries as the original, or the charcoal from the same trees, and so on and so on. Again, no new machines would ever get built. Before studying how any ancient machine worked, we might want to define what that work actually was. In the case of ballistas the work they performed was to project lethality. That is the most important work-related function of the device. If we really want to understand these machines it should be the one vital talent our carefully qualified analogs seek to emulate. End of blurb... Now I have said all that, I think I shall retire from this subject as I've no wish to beat a dead ballista. Please feel no obligation to respond. I respect your work and there is no need for us to agree on everything. Nick Nicholas Watts (talk) 02:36, September 16, 2015 (UTC) Welcome Hi, welcome to ! Thanks for your edit to the File:End cap 5.jpg page. Please leave a message on my talk page if I can help with anything! Samuli.seppanen (talk) 17:09, September 14, 2015 (UTC) Hi again, Two questions before my monologue # How many kilos of cord do you have in your Firefly torsion spring? # What kind of bolt kinetic energy have you got with that configuration? I could use this knowledge to calculate what kind of energy levels I can realistically expect from the Cheiroballistra. Your approach to reconstruction (the blurb) is most sane. I would just add that keeping as close as possible to ancient manufacturing techniques yields information which would get lost if all the parts were machined. That said, even I wouldn't go as far as making my own charcoal and producing my own iron from iron ore :). I'm content with "wasting" time making every part 2-5 times until I understand why certain approaches work and which don't :). The end result is usually beautiful in its simplicity and elegance. For example, the little ladder/arch locking mechanisms, my T-clamps and the elliptically tillered throwing arms work so well, are so simple and match the text and diagrams so closely that I can confidently say "this is how the must have been made". That, of course, does not rule out other solutions for other types of machines. Basically the only objection I have to the vernier plates is that none have been found in archaeological record and none are mentioned in the cheiroballistra text. In particular, the Lyon find (Baatz 1981) includes both the field-frame and the matching iron washers, but no vernier plates: The Lyon kambestrion has 4 holes in the hole carrier like the Elenovo find. Unfortunately the number of holes in the washers is omitted in the text, and while the picture shows probably 6 holes, some of them have rusted shut or are assumed to have been there. Seeing the real artifact(s) would help a lot. My cheiroballistra has 6 holes in the washers and 8 pairs of holes in the hole carrier. As I said, I (can) only use half of those hole carrier holes due to impreciseness of my manufacturing method (=forging), so in practice my hole carriers have usable 8 holes (not pairs). So the Lyon setup (4+6 holes) has half of the rotational granularity of my cheiroballistra. Interestingly I had the "Lyon configuration" in my now-discontinued old field-frames, and it did seem too little. It was rather tricky to tune the arms just right, and I think more granularity is needed. At some point I will plug half of my hole carrier holes close, so that I simulate the Lyon configuration and see if it is hopeless or not. In conclusion: you may be right with your vernier plate theory, but I don't think all the other options have been exhausted quite yet. Anyways, tomorrow I'll head to the forge to add stell back to the curves of my field-frames, and to reinforce my little ladder tenons which have bent. Maybe I'll make another, stronger little ladder plus matching T-clamps while I'm at it, just in case. Then I can restring the torsion springs to 350hz which makes the torsion spring twice (1.96x) as strong given the same amount of rotation. I suspect that that amount of pretensioning is just about right and should easily give let me go from 85 joules to 100+ joules easily, without any increase in strain on the parts (except the field-frames, of course). Samuli.seppanen (talk) 08:46, September 16, 2015 (UTC)